Class 8 same-dealer used truck sales volumes increased month-over-month with a third sequential double-digit rise, according to data tracked by ACT Research.

Meanwhile, retail sales of heavy-duty natural gas trucks in the U.S. and Canada posted a “healthy start” to 2017, the firm said, boosted mostly from refuse fleets, transit, and school bus operators.

“The best January in the past three years set up the positive year-to-date February performance,” noted Steve Tam, ACT’s vice president, in a statement “Among truckers, it appears as though the majority of incremental volume came from those who currently have natural gas vehicles and are replacing units or increasing their number.”

Back on the used Class 8 side of the ledger, total volumes also showed improvement in long-term comparisons, up year-over-year when compared to last March, and year-to-date compared to the first three months of 2016.

On top of that, the used Class 8 retail segment, as well as the used Class 8 auction and wholesale markets, witnessed month-over-month increases, too, Tam pointed out.

“From a micro perspective, all signs are pointing north with all three market segments posting sequential improvements in all time comparisons,” he noted.

“Despite year-to-date actuals, we believe 2017 used Class 8 truck sales will see a small decline from 2016,” he explained. “Elusive freight growth and lower new truck sales are the basis of the assumption.”

Where natural gas trucks are concerned, in comparison to the total market, Class 8 and bus sales remain slow when calculated as a percentage of the total market.

For 2016, the natural gas share was estimated at 3% due to the higher new truck sales and lower natural gas penetration.